The ultimate objective is to elucidate more fully the nature of the cellular defects in blood and marrow in paroxysmal nocturnal hemoglobinuria (PNH) in relation to in vivo and in vitro aspects of PNH. We will extend previous studies involving assessment of hemolysis, iron metabolism, with various agents and the effects of chronic hemolysis and thrombosis on organ function and structure. Laboratory investigations will predominantly concern: 1. the mechanism of the sucrose hemolysis test; and 2. nature of the membrane defect in PNH. We propose that a structural change occurs in a serum protein in the serum-sucrose mixture, which allows normal serum protein(s) to behave like an "antibody" and thus initiate hemolysis by the complement pathway. We will attempt to separate and characterize this "active" protein component. Available evidence suggests that the PNH red cell defect involves membrane proteins. AChE activity on the single cell level will be further assessed using histochemical staining. Normal and PNH RBCs will be treated with drugs known to affect microtubules and cause rigidity of the cell membrane and then tested in various PNH hemolytic systems. Another possible explanation of the membrane defect in PNH (esp., hepatic venous thrombosis) in terms of platelet and coagulation abnormalities. One of our theses is that thrombosis in the microvascular circulation in PNH brings about organ changes strikingly similar to (albeit milder than) those seen in sickle cell anemia.